Method of utilizing piperidine as a condensate corrosion inhibitor

ABSTRACT

A METHOD OF AND DOSAGE CONCENTRATION FOR INHIBITING CO2 AND O2 CORROSION IN BOILER STEAM CONDENSATE SYSTEMS COMPRISING ADDING PIPERIDINE IN CONDENSATE CONCENTRATIONS OF FROM ABOUT 1.0 TO 10.0 P.P.M. TO ACHIEVE A PH OF ABOUT 8.8 TO 9.5 THIS METHOD PROVIDES ADEQUATE LPROTECTION ESPECIALLY FOR THE FERROUS METAL PIPES NORMALLY UTILIZED IN CONDENSATE SYSTEMS AND UTILIZES A REAGENT WITH A FAVORABLE DISTRIBUTION RATIO BETWEEN VAPOR AND INITIALLY FORMED CONDENSATE.

Patented Aug. 17, 1971 3,600,125 METHOD OF UTILIZING PIPERIDINE AS ACONDENSATE CORROSION INHIBITOR Kenneth G. Phillips, River Forest, Ill.,assignor to Nalco Chemical Company, Chicago, 111. N Drawing. Filed May16, 1969, Ser. No. 825,395

Int. Cl. C23f 11/04, 11/08 US. Cl. 212.7 4 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a novel treating compound which isuseful in inhibiting corrosion in return steam condensate lines. Moreparticularly, the subject invention is directed to a member of a groupof cyclic saturated imines known as pentamethyleneimine or piperidine.

It is well known that steam lines and steam condensate lines are subjectto corrosion which is very diflicult to control. This corrosion isapparently due, to a large extent, to carbon dioxide and oxygen in theboiler-steamcondensate system. Carryover from the boiler water can alsoincrease the corrosion. The problem of corrosion of the internalsurfaces of steam condensate return lines has been recognized for manyyears. Generally, the difficulties that have been experienced arepitting, grooving and ultimate deterioration of sections of thecondensate return system and the plugging of constrictions in the systemwith the insoluble products of corrosion. To evaluate properly theactual cost of return line corrosion, it is necessary not only toconsider the loss in terms of labor, curtailed production and the costof the material destroyed, but also to weight effects in terms ofinefficient operation of fouled equipment.

Experimental studies by various investigators indicate that dissolvedcarbon dioxide and oxygen are responsible for practically all thecorrosion in the condensate lines. The various expedients that have beendevised for combating this attack are as follows:

1) The use of corrosion resistant alloys, which is generally prohibitivefrom a cost standpoint.

(2) Minimizing the amount of carbon dioxide and oxygen in the condensateeither by venting or pretreatment of the boiler feedwater.

(3) Chemical treatment of the condensate.

It has been found that a readily volatile alkaline base compound may beutilized for the treatment of steam condensate return systems andexamples of prior art treatments of such systems are found in 2,582,138Lane et al., 2,956,889 Denman, 3,029,125 Hummel, 3,378,581 Hummel.

Additionally, the use of other imines such as hex-amethyleneimine as acorrosion inhibitor but in a strongly acid medium has been described andtaught in 3,091,591 Hackerman et al., but the problem of the dosageconcentration and monitoring of the pH level in a restricted alkalinerange is not suggested by this teaching. Furthermore, the favorablequalities of piperidine in the concentration utilized imparting thermalstability,

high pH producing ability, and favorable distribution ratio in theinitially formed condensate all militate for novelty in the presentdevelopment.

Pursuant to the present invention, it has been found that corrosion inthe steam and condensate return systems may be lowered or substantiallymitigated by treating such systems with a dosage or corrosion inhibitingamount of piperidine. This material is effective when added either tothe boiler feedwater, to the steam lines, or to the condensate returnlines, but due to the economics and wastage in the other methods, it ispreferred to add the treatment to the steam condensate line since it isthis part of the system where corrosive attack is the severest and thesmallest amounts of the treatment are the most effective. The amount ofpiperidine added should be at least 1.0 part per million (ppm) of thecorrosion inhibiting chemical by weight of the steam of steamcondensate, preferably 1.0-10.0 p.p.m., and even more preferably 1.04.0ppm. The dosage Will, of course, vary depending upon the conditions ofthe system and other variable factors; hence, dosages as high as 50p.p.m. may be necessary under extraordinary corrosion conditions.

The employment of the corrosion inhibiting chemicals in accordance withthis invention is applicable to the generation of steam at varioustemperatures and pressures. Good results can be obtained where steam isgenerated under atmospheric conditions, subatmospherie conditions orsuperatmospheric conditions. In most cases, steam is generated atpressures from atmospheric up to 1500 pounds per square inch or more andthe corresponding temperatures.

Piperidine has the following formula:

on fun zs It was found from the experimental data that the piperidineappeared to collect preferentially in the initially formed condensate sothat it acted to neutralize the freshly carried over CO and apparentlyacid in a similar fashion as a few other reagents such as morpholine inthis connection. Thus, a good distribution ratio for the reagentindicated that the greatest portion of the reagent settles in the waterphase of the initially formed condensate providing corrosion protectionrapidly at the liquid/metal interface.

In the operation of an on stream boiler system for steam condensatereturn, it has been found that a reagent should be utilized in dosageconcentrations sufficient to impart or raise the pH level of theslightly acid initial condensate to the alkaline range and preferably toa pH of about 8.8-9.5. A pH level above 9.5 is not deleterious to thesystem, but efiiciency and cost consideration make it an unpreferredmodus of operation. A pH value below about 8.8 begins to subject the system to corrosion damage principally from the carryover CO and defeatsthe mission of the corrosion inhibitor reagent employed. In on streamboiler usage, the present system preferably contemplates incrementaladdition of reagent to permit monitoring and maintaining of the pHwithin the desired alkaline bracket. It is to be noted that the presentreagent also has favorable stability characteristics in this setting,which unlike many other nitrogen base compounds permits utilization inthe severe heat and acid conditions without breakdown of the reagent.

It has also been found that the narrow range of a pH of about 8.8-9.2 isoptimum in this connection of steam condensate return systems. Thus, amonitoring system employing the reagent at this pH is one which willoperate at the greatest efficiency.

Example 1 P.p.m. P 200-250 NaCl 1400-1600 D.S. 2600-3200 P 40-60 80;,40-60 A Milton-Roy mini-pump was set up so that the treatment solutioncould be injected directly into the feedwater line at a point near thefeedwater storage tank and input to boiler feed pump.

Live Steam was throttled from a take-01f line and passed through anInconel steam sampling coil where it was condensed and cooled to 4050 F.at a rate of 100-300 ml. per minute.

The cooled condensate was passed continuously through 0.1 cell constantpencil type conductivity cell which was connected to a Baileyconductivity recorder using 24 hour round charts with a range of 0-50micro mhos.

After passing through the conductivity cell, the condensate entered thepH flow cell which consisted of a polyethylene cup (3 dia. x 3 /2" deep)into which standard laboratory pH electrodes were immersed. Condensateentered near the bottom of the cup and overfiowed near the top.Measurement of the pH was by a Beckman Zeromatic pH meter which wasconnected to a 24 hour round chart Foxboro pH recorder. The open pH flowcell was kept shielded from dust by a paper covering.

Samples of condensate were collected daily to be analyzed for copper,iron, ammonia, and amine content.

Treatment chemicals.-In preparing the amine solutions used as treatment,piperidine was utilized from commercial sources. The diluted treatmentsolutions were fed from a 2 gallon calibrated glass bottle.

Results.Data indicated that about 1.5 p.p.m. of piperidine produced a9.0 condensate pH.

In other tests giving similar results when the plant boilers wereoperating with a steady load and about 25% makeup, about 1.0 to 4.0p.p.m. of piperidine, based on total steam flow, was needed to give acondensate pH of 8.8-9.0.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of inhibiting the corrosion of steam condensate lines causedby C0 and O in the steam condensate which comprises adding to thecondensate in said lines a small but effective amount of piperidine toraise the condensate pH level to a range of about 8.8 to 9.5.

2. The method of claim 1 wherein the pH level is raised to a range ofabout 8.8 to 9.2.

3. The method of claim 1 wherein the pH of said condensate is maintainedand monitored at about a pH of 8.8 to 9.5 by addition of incrementalamounts of piperidine while said steam condensate line is on stream.

4. The method of claim 3 wherein the condensate system is maintained andmonitored at a pH of about 8.8 to 9.2.

References Cited UNITED STATES PATENTS OTHER REFERENCES Rosenfeld, I.L.,et al.: Corrosion, July 1964; vol. 20, No. 7, pp. 222t to 234t.

Hackhs Chemical Dictionary, Third Edition, 1944; p. 662 relied on.

Sperry, S. M.: Combustion, November 1955; vol. 27, No. 5, pp. -67 and 71relied on.

MORRIS O. WOLK, Primary Examiner B. S. RICHMAN, Assistant Examiner U.S.Cl. X.R. 2l2.5

